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A large amount of waste activated sludge (WAS) and food waste (FW) are produced every year in China. Anaerobic co-digestion is considered to be an effective way to solve this problem. This study applied FW/WAS mixture as co-substrate to create different digestive environment, aiming to understand the mechanism of Fe3O4 particles in promoting AD performance. The results showed that the addition of Fe3O4 presented various performances when facing different digestive acidification stress brought by different mixing ratios of WAS and FW. Methanogenic pathways and microbial communities varied with substrates’ properties. For group A (WAS mono-digestion), the acetoclastic methanogens dominated, 20 mg/g VS (according to the iron element) Fe3O4 could promote methane production, while 200 mg/g VS Fe3O4 would inhibit microbial activity. The promoted methane production by Fe3O4 was attributable to the promotion of sludge hydrolysis. For group B (WAS: FW = 1:0.5, based on VS addition, similarly hereinafter), Fe3O4 triggered direct interspecific electron transfer (DIET) between bacteria and methanogens. For group C (WAS: FW = 1:1), the hydrogenotrophic methanogens dominated, bacteria excreted more non-conductive polysaccharides in EPS to resist unfavorable environment, thereby it prevented their contact with Fe3O4 particles. So, it was difficult for Fe3O4 to trigger DIET and promote the digestive performance of batch experiments in such condition.

Non-hemolytic enterotoxin (NHE), a tri-partite, proteinaceous toxin encoded by contiguous nheA, nheB and nheC genes of Bacillus cereus sensu lato (B. cereus s.l.), is considered to be associated with the foodborne diarrheic syndrome. However, B. cereus s.l. includes a number of closely related strains, and the occurrence of NHE among them, and other members of Bacillus is unclear. Consequently, we aimed to determine the distribution and evolution of NHE within Bacillus by confirming the presence of the nheA, B and C sequences and variation within them using published data, and to analyze the genomic and genetic diversity. The phylogenetic tree of NHE proteins (NheA, NheB and NheC) from 81 different B. cereus s.l. strains was constructed. And on the genetic determinants of the NHE toxin did not bring any obvious link between the nheABC genes sequence of a strain and its virulence in the diarrhoeal pathogenesis. Analysis of the genomic diversity of the nheA, B and C loci revealed that their upstream regions were more conserved than the downstream sequences. Multilocus sequence typing schemes (MLST) based on seven concatenated housekeeping genes and nheA, B and C genes of the 75 strains were developed. The neighbor joining phylogenetic tree based on seven housekeeping genes together with nheA, B and C genes was similiar to published Bacillus phylogenetic trees. And on the genetic determinants of the NHE toxin did not bring any obvious link between the nheABC genes sequence of a strain and its virulence in the diarrhoeal pathogenesis.The results indicate that nheA, B and C genes do not affect the diversity of housekeeping genes, and this specific NHE protein does not participate in the diarrheic syndrome. Electronic supplementary material The online version of this article (doi:10.1007/s00203-017-1350-9) contains supplementary material, which is available to authorized users.